The present invention relates to an electromagnet assembly for use in connection with electromechanical valve actuators and a method of assembling an electromagnet for use in connection with electromechanical valve actuators.
As engine technology advances and manufacturers strive to increase engine power, improve fuel economy, decrease emissions, and provide more control over engines, manufacturers are developing electromechanical valve actuators to replace cam shafts for opening and closing engine valves.
Electromechanical valve actuators allow selective opening and closing of the valves in response to various engine conditions. Electromechanical valve actuators generally include two electromagnets formed from a lamination stack and with embedded power coil. A spring loaded armature located between the electromagnets is movable between the electromagnets as the power coils are selectively energized to create a magnetic force to attract the armature. The surface of the electromagnets to which the armature is attracted when the power coil of an electromagnet is energized is generally referred to as a pole face. The armature is attached to the valve so that as the armature moves between pole faces in pole-face-to-pole-face operation, the valve is opened and closed.
Electromagnet assemblies for electromechanical valve actuators are traditionally formed by assembling two electromagnets, each having an electric coil, into a housing. The electromagnets are formed by laminating a plurality of magnetic laminae to form a lamination core. Each laminae is interlocked with the adjoining laminae with the use of tabs on each laminae. In some cases, various holes are machined into the lamination core providing, for example, for armature stems.
With the lamination core formed, a power coil may be inserted within a coil cavity on the lamination core. The power coil is held in place by filling voids in the cavity with epoxy. The assembled electromagnets are then secured to a housing. In some cases, the housing includes the use of c-channels with fasteners. For example, the electromagnet may be bolted to the c-channel, or a bolt may pass through a passage on each side of the electromagnet and couple the electromagnet to each side of the c-channel. Properly positioning the electromagnets within the c-channels during assembly is difficult due to various tolerance stack ups. In most cases, the positioning requires the use of location features such as pins or encapsulants. Properly assembling the c-channels into a complete electromechanical valve actuator with the armature plate between the electromagnets so that the pole faces of linear electromagnets are parallel with the armature plate and so that the stem passages in the closed electromagnet and open electromagnet are aligned is difficult and time consuming. Any misalignment of the armature stem passage creates excessive wear and friction caused heat.